In many agricultural regions, deep-water wells are heavily relied upon to provide the water necessary to irrigate crops. In large-scale operations, these deep-water wells, which may be 1200-1300 feet deep, supply large volumes of ground water to the surface through deep well pumping systems. Currently available systems, however, suffer from one or more drawbacks that increase operation and maintenance costs.
Traditionally, for large-scale deep-water wells, centrifugal pumps have been installed. A centrifugal pump is a rotodynamic pump that uses a rotating impeller to increase the velocity of a fluid. Generally, one or more cascaded multi-stage impeller pumps, or “bowls” as the stages are commonly called, have been used for approximately every 70 feet of well depth. Accordingly, a well that is 500 feet deep requires at least seven bowls situated at the well bottom to be effective. These pump systems are driven either by a large down hole submersible electric motor or by a complex mechanical drive from the surface. The latter is typically powered either by a vertically oriented electric motor or by a gasoline or natural gas engine driving through a speed reducer gearbox and a ninety-degree drive.
Centrifugal pumps have several drawbacks, however. For example, centrifugal pumps are driven at about 1750 rpm such that, with an eight-inch pump as is commonly used, the impeller tip speed moves in excess of 42 miles per hour. As a result, even small grains of sand or other contaminants can cause rapid wear or even catastrophic failure. Another drawback of centrifugal pumps is that they must continuously maintain a certain minimum rpm before they will pump any liquid at all. A typical centrifugal pump designed for deep well water use will cease pumping altogether if its rotational speed falls below about 1550 rpm. A further drawback of centrifugal pumps is that their speed cannot be controlled as needed. It would be desirable to have a pumping system that can pump, for example, at anywhere from 500 rpm to 1800 rpm as needed.
Maintaining centrifugal pump systems can also be time consuming and expensive. For example, for a centrifugal pump system placed in a 600 foot deep well and powered by an electric motor, electric costs can be over $5500 per month. For the same size well, using an internal combustion engine to power the pump requires daily maintenance and about $4000 in fuel each month. Additionally, periodic overhauls of the internal combustion engine cost approximately $3000. It would be desirable to use instead a more cost effective and lower maintenance pump, such as a positive displacement pump, for large-scale deep-water well applications.
Positive displacement pumps have not been traditionally used for deep-water well applications because deep wells require too large of a pump. Positive displacement pumps include piston pumps, sucker pumps, and plunger pumps. For example, plunger pumps generally use mechanical or electrical energy to raise and lower a reciprocating plunger in a cylinder. As the plunger is forced to the bottom of the cylinder, the plunger collapses and allows a fixed amount of fluid to move from the bottom of the cylinder to the area above the plunger. The plunger is then pulled out toward the top end of the cylinder and consequently draws fluid in the bottom of the cylinder below the plunger. The plunger forces the fluid above it to flow upwards through the cylinder and well bore to a discharge field or zone. Generally, the amount of water discharged is dependent on the stroke length of the pump. It would be desirable to develop a pump where the amount of water discharged is not limited by the stroke length of the pump.
Another drawback to positive displacement pumps for use in deep underground aquifers is that a long vertical cylinder must be used. While in shallower applications, the momentum of the fluid is sufficient to carry it out of the well bore, in deeper applications, the momentum may be insufficient. Consequently, the fluid will not be pumped out of the well bore because the piston cannot lift the weight of the fluid in the cylinder and that above it. In general, pumps have to be designed taking into account the head pressure. Head pressure is the amount of pressure due to static and dynamic fluids sitting above the pump. The static head pressure relates to the elevation of the fluid above the pump, and the dynamic head pressure relates to the velocity of the fluid above the pump. Bernoulli's equation for determining head pressure isH=static pressure head+dynamic head+elevationorH=p/dg+v2/2g+y where p is pressure in lb/in2 or kPA; d is density in lb/ft3 or kg/I; v is velocity in ft/sec or m/sec; g is gravity (32.2 ft/sec2 or 9.8 m/sec2); and y is elevation in ft or m. Accordingly, it would be desirable to provide a high capacity positive displacement pump that eliminates or significantly reduces the head pressure so that fluid can be efficiently and cost-effectively drawn from deep wells and underground aquifers. It would also be desirable to provide an efficient high capacity positive displacement pump that can remain in service for long periods of time without significant maintenance and that is fueled by alternative energy sources.
Therefore, it is an object of this invention to provide a positive displacement pumping system for use in deep wells that is not limited by the stroke length of the pump. It is a further object of this invention to provide a positive displacement pumping system with significantly reduced head pressure. Another object of this invention is to provide a positive displacement pumping system that requires little or no maintenance after installation. It is also an object of this invention to provide a positive displacement pumping system that can be powered by solar or wind power. A further object of this invention is to provide a positive displacement pumping system where speed can be controlled or slowed down as needed.